Customers shopping for Apple Inc.'s iPhone might pay little attention to the gadget's "slide to unlock" feature, but you would never know that from a quick glance at Apple's current roster of patent lawsuits.

The technology giant has secured two key U.S. patents on slide-to-unlock—a technology that lets users wake a dormant phone with a finger-swipe across the screen. And it is wielding those patents like swords against rivals around the world.

In recent months, Apple has sued HTC Corp. in Delaware and Germany over one of those patents and others. It has used the patents to fight back against suits Motorola Mobility Holdings Inc. MMI 0.00% filed against it in Miami and Germany. And it has invoked them in lawsuits against Samsung Electronics Co. in Australia, the Netherlands, and San Jose, Calif..................At the center of the war is slide-to-unlock. It dates to late 2005, more than a year before Apple announced a product with a touchscreen.

Three diagrams from a patent awarded in 2012 to Swedish company Neonode that surprised both Apple and Samsung. Neonode first made its patent claim in 2002, three years before Apple's application.

The first iPhone was in the works at the time, and Apple's software engineers, including one of its current senior vice presidents, Scott Forstall, felt the need for a feature that would prevent the phone from accidentally making a call or sending a text message when pulled from a pocket or jostled in a purse.

Apple's engineers regarded slide-to-unlock as important because it flavored a user's first experience with the device, according to a person familiar with the matter. The team tried many iterations, this person said, from different finger-swiping speeds to different-shaped motions.

Two days before Christmas 2005, Apple filed a patent application with the U.S. Patent and Trademark Office containing a handful of rudimentary drawings with ovals and circles.

The diagrams showed an early version of the design that current iPhone models use: a white rectangle with rounded edges that, when touched and dragged to the right, slides alongside a horizontal channel until the device "unlocks" and opens to the home screen..................Several months later, Apple asserted claims against Motorola in Florida, where Motorola was already suing Apple, alleging that over a dozen Motorola products violated Apple's slide-to-unlock patent.

The slide-to-unlock used on many Motorola phones resembles Apple's in many ways. Users open the phone by dragging a finger from left to right across the bottom of the phone's screen. But the visual representations of the sliding motion are somewhat different.

Apple users see a white rectangle move across the screen while, with the Motorola phones, the slide of a finger extends a bar across the screen. Partly for this reason, Motorola claims its so-called "stretch to unlock" doesn't infringe Apple's patent.

Samsung's Circle

Samsung, however, posed a unique challenge for Apple on slide-to-unlock. While Apple was waiting for its patent to be issued, Samsung unveiled phones that opened when a user touched the center of a circle on the screen, and dragged a finger to any point outside the circle.

Samsung's design was different, but in the mind of Apple executives, not different enough. So, in 2009 Apple went back to the patent office, according to a person familiar with the matter, and asked for a patent that would cover a wider variety of slide-to-unlock designs.